One of the current methods of detecting organic and inorganic particles relies upon the use of channels in combination with a sensing medium to detect the presence of a particle. Where a particle is trapped in the channel, one of more physical properties of the sensing medium is affected. Thus, in WO 2005/071393 a particle detecting device is described in which a fluid microchannel is provided on a substrate. Multiple particle trapping sites are provided within the microchannel with particle specific, trapping substances provided on the surfaces of the microchannel at each trapping site. Trapped particles are identified using, for example, fluorescent labels which bond to the trapped particles.
Similarly, biological detector chips are known in which an array of oligonucleotide probes, for example, are immobilised on a planar substrate such as that described in U.S. Pat. No. 5,861,242. The surface of the detector chip is then exposed to a sample, which may contain the biological particles of interest, and where the biological particles are present these are trapped by bonding to the oligonucleotide probes. Here too, optically active labels are used to bond with the trapped biological particles, for the purposes of identification.
Also, detectors are known for use in identifying the presence of ions in a bulk sample solution such as the ion sensitive field effect transistor (FET) sensor described in WO 2005/073706.
These known detector arrays have the disadvantage of being inherently designed to be highly sensitive to specific biological particles and insensitive to all others. Frequently, however, detection of many different particles is desired. There is, therefore, a perceived need for a detector capable of identifying the presence of a number of different particles, chemical species or biological organisms in a sample.